Numerous innovations for tire pressure sensors have been provided in prior arts.
Pressure sensors have long been used to monitor tires for determining whether the tire was properly pressurized. Known methods for monitoring tire pressure included:    (a) A pressure sensor module installed inside the tire on the rim and secured by a steel mounting bend, and transmitted the pressure data by wireless RF signals to a monitor located in the driver cab of a vehicle. With this method, system installation and replacement are very inconvenient and labor intensive. The tire must be removed prior to and then remounted after sensor installation. The sensor might break if the band was fastened too tightly or be damaged by the tire bead during tire remounting. RF signal transmission would be blocked and weakened by the steel belts embedded inside the tire. The mounting bend might become loose and break.    (b) A pressure sensing and transmission device mounted on the inner end of a specially designed tire valve, and transmitted the pressure data wirelessly to a monitor. With this method, sensor installation or replacement also involved the inconvenient and labored manipulation of the tire. RF signal transmission would be blocked and weakened by the tire wall. Additionally, the inability of using conventional valves limits the application of this method to only a narrow range of wheel types that can fit with the specially designed sensor valves.    (c) A pressure sensing and transmission device mounted on the valve stem outside of the tire. The device measured tire pressure through the valve and transmitted pressure data wirelessly to a monitor. This method has the advantages of easy installation and good signal transmission. With this method, however, the user must remove the sensor to refill tire air and then reinstall the sensor back on the valve stem. In addition to the inconvenience, frequent sensor removal and reinstallation would damage the air seal and cause air leak, thereby creating a safety hazard for the user.
U.S. Pat. No. 4,804,808 issued to Dal Cero on Feb. 14, 1989 discloses a pressure-sensing device that senses low tire pressure and signals low pressure using a transmitter and a receiver.
U.S. Pat. No. 5,289,161 issued to Huang on Feb. 22, 1994 discloses a pressure gauge having a diaphragm that pushes a spring-loaded rod between two switch devices which, when the tire is not properly pressurized, will trigger the sending of an encoded RF signal to a receiver for generating alarms.
U.S. Pat. No. 5,694,111 issued to Huang on Dec. 2, 1997 discloses an encoder unit and a transmitter circuit for a tire pressure sensor device for generating encoded RF signals received by a receiver with a display unit.
U.S. Pat. No. 4,319,220 issued to Pappas on Mar. 9, 1982 discloses a system for monitoring tire pressure of the tires having respective transmitters communicating alarm signals to a receiver.
U.S. Pat. No. 5,001,457 issued to Wang on Mar. 19, 1991 teaches a cab mounted monitor having a graphic display for visually indicating under-pressurized tire, which is identified by encoded signals transmitted from respective tire pressure sensing transmitters to the cab mounted central receiver.
U.S. Pat. No. 6,535,116 issued to Joe Zhou on Mar. 18, 2003 discloses a pressure-sensing valve stem mount miniature sensor for a vehicle monitoring system.
U.S. Pat. No. 6,799,455 issued to Neefeldt, et al on Oct. 5, 2004 discloses a pressure-sensing valve mount device that includes an antenna extending through the valve passageway into the tire for transmitting RF signals.
U.S. Pat. No. 6,993,962 issued to Ko on Feb. 7, 2006 discloses a pressure-sensing valve mount device using a electrically conducting pinch pin for power supply when the device is screwed on the tire valve.
Typically, these systems teach tire valve mounted pressure sensors responsive to individual tire pressures for generating encoded signals transmitted to a receiver with graphic displays. However, these teachings do not address or not able to resolve many practical issues, as described below:
(i) Valve Stem Mounted Sensor with Air-flow-through Function
A tire valve-stem mounted pressure sensor must be easy and safe to use. Properly pressurized tires are utmost important for safe driving and for prolonging the life of tires. However prior systems generally must be removed for refilling tire air and, therefore, are very inconvenient for tire maintenance. In addition, frequent removal and reinstalling a sensor would damage its air seal and consequently cause air leak, thereby creating a safety hazard. It is technically very challenging to make a small external sensor that can support tire air refill without removing the sensor. Prior teachings generally do not present practical methods to make small external sensors with air-flow-through function.
(ii) Valve-stem Mounted Sensor with Security Lock
A valve-stem mounted pressure sensor is generally secured by screwing on the tire valve stem thread. Constant vibration of a moving vehicle might gradually loosen the grip of the sensor on the valve stem. The sensor also might be loosened and detached from the valve stem of a fast moving vehicle due to forces exerted by tire rotation and airflow. External sensor is easy to install and remove so sensor thief is a problem for the user. Prior teachings generally do not address methods for protecting the installed sensors.
(iii) External Sensor with Manual Signal Triggering Function
Tire monitoring system programming and services require learning the sensor measurement data from a stationary vehicle. A common practice of inducing an external sensor signal is by removing and then reinstalling the sensor. This method would potentially damage the air seal and cause air leaks. Prior teachings generally describe methods of using a magnet or low frequency (LF) signals to energize the sensor for producing a signal. These methods require additional electronic components and circuitry in the sensor and therefore would increase its size and weight; the methods also require extra hardware such as a magnet or a LF initiator for triggering the signals. External sensors must be small sized with a small battery so a manual signal triggering method without extra electronic components is very important and useful.
(iv) External Sensor Detects Motion without Motion Detecting Circuitry
Most tire monitoring sensors use battery to drive the electronics and must conserve power consumption for prolonging sensor life. Prior systems generally use motion detecting circuitry to detect vehicle motion for activating or increasing tire monitoring activities, and to decrease or cease monitoring when the vehicle is at rest. These methods require additional electronic components and therefore would increase size and weight to the sensor. Mechanical motion detectors require proper orientation to be effective, whereas solid state motion detectors have large power draw and easy to break. External sensors must have a small size with a small battery so a motion detection method without motion detecting circuitry taking up space and power draw is very important and useful.